Process for the production of carboxylic acids



Uni ed Stat s P n o i TROCESS FORTHE PRODUCTION OF CARBOXYLIC ACIDS Herbert Koch, Mnlheim an der Ruhr, and Wilhelm vHu'islten, 'Essen', Germany, assignors to Studiengesell- .schaft Kohle mit beschriinkter Haftung, a corporation of Germany No Drawing. Application May 12, 1955 Serial No. 507,998

Claimspriority, application Germany May '15, 1954 i I 12 Claims. (Cl. 260-413) I This invention relates to :a process for the production otcarboxylic acids.

The/subject of patent application Serial No. 342,961, filed March 17, 1953, now Patent No. 2,831,877, is the {PFDdUCtlOIlROf carboxylic acids from olefines and carbon monoxide in the :presence of catalysts .such as sulphuric acid .or hydrogen fluoride, the reaction initially being carried out .the liquid phase Without .the addition .of water .in the presence of catalysts which contain only a small amount of water or which if desired are .even anhydrous, more especiallyacatalysts such-asst leastr90% ,sulphuric .acid, .or anhydrous hydrogen fluoride :by itself or with the addition of boron fluoride, whereupon the reaotion product is then absorbed in water and worked ,up :inknown manner. I

When using this'method, at .least three .mols of sul- ;phur'ic acid must be used for the reaction-of 1 .mol of solefine, and -even 5 to .10 mols of sulphuric acid it pervticularly good yields .of carboxylic acid-are xto be ,pro- -duced. Tlhese dataapplyas regards .norrnal unbranched olefines, .for example propene, :n-butene and .the two zn pentenes. With the branched claims, for example with :the iso-butene, the conditions are somewhat more favourable, that is to say, it :is ,possible to manage with a smalleriamountof sulphuric acid. When working with sulphuric acid, however, itis necessary to .dilute strongly .with water .when the reaction :is complete in order that ,the carboxylic acid formed may :be separated .from its .mixture with .the sulphuric acid. Consequently, .it .is

necessary ,for large amounts ofdilute sulphuric acid to ".be constantly .re-concentrated. This concentration of @sulphuric acid is made difficult or even quite impossible by .the .fact that hydroxysulphonic acids .are formed on a more .orless large scale as a secondary reaction in addition to :thecar'boxylic acid tsynthcsised. Ihese hydroxyiSliLPhQIliC acids cannot easily be separated from sulphuric acid and, when .the sulphuric acid is concentrated by i evaporation, from .a certain stage @of concentration they ,cause .carbonisation -or tar .formation of .the acid with evolution of sulphur dioxide. 'Instead of a simple concentration process, it *istheretore necessary in certain cases do ,envisage a complete regeneration .of the :sulphunic acid, and ,processes which .have provedsatisfactory .from ,a. technical point of .view alreadyexist for this ,purpose. ":However, it is not possible to avoid a .con- ,siderable :increase in :the production costs due to these processes.

A large :number of experiments have been conducted with the object ofpreventing the disturbing formation of .hydroxysulphonic .acids. In this connection, success has .been achieved in substantially obviating the formation of hydroxysulphonic acid, particularly by using flow reaction temperatures in .the region of about 10." and lower; Nevertheless, the small amounts of hydroxysu'l- ,phonic .acid still .being .formed .result in carbonisation of the sulphuric .acid when .it .is .being reconcentrated.

I It has now been "found that, whereas formerly 'it was 2,876,241 Patented Mar. 3,

necessary to .dilute the reaction product with a large amount of water after the incorporation of the carbon monoxide when using concentrated sulphuric acid,.the.car- -boxylic acid obtained in a very good yieldfrorn olefines, preferably tertiary olefines, for example isohutent," 2- methyl pentene-l, Z-ethyl 'hexene-l and other olefines branched .on the double bond, can beseparated smoothly without this dilution with water if the catalysts .used consist of monohydroxy fluoboric acid H(BF OH) or'its complex mixtures with inorganic acids, for example phosphoric acid or sulphuric acid. The reaction of the olefines proceeds exceptionally smoothly and quickly, and after the first part of the reaction, i. e. the incorporation of carbon monoxide, has been completed, it is sufficient if only that amount of water which is stoichiometrically necessary is added in order to effect the separation of the carboxylic acid from the catalyst, which can be used again. Accordingly, the present invention provides a process for the production of carboxylic acids from cilefines, preferably olefines branched at the double 'bond, and carbon monoxide, in the presence of catalysts con taining inorganic acids and boron fluoride, wherein the reaction is initially carried out in the liquid phase Without the addition of water in the presence of a catalyst comprising monohydroxyfluoboric acid or a mixture thereof with phosphoricacid or sulphuric 'ac'idwhidh contains no water or a small amount of water, and only then is the stoichiometric amount of water required izor the-reaction added.

These complex compounds of boron trilluoride with inorganic acids which are to be used in the processdt the invention have already been described as suitable 'catalysts for the reaction of aliphatic alcohols with carbon monoxide to form organic acids. In this case, however, 'very strict working conditions are used andthe operation is carried out at a temperature between 150 and 400 C. and a pressure between .25 and 900 .atm. [There is thus the possibility of introducing olefines instead of the alcohols. in this case, .it is, however, essential thatsteam be :added if acids are .to be produced.

.Tzhe complex compounds of boron .trifluor'ide with 'inorganicacids, for example phosphoric acid, which are to be used in the process of the invention in the absence of water or in the presence of a small quantity .of water, enable olefines, preferably olefines branched at the double bond, to be reacted with carbon monoxide to form .carboxylic acids under very mild reaction conditions, .such -as temperatures which are advantageously at .or below 00m temperature and pressures which are not higher than atm. .and which are preferably between Siland 100 atm.

When using the process according to the invention,

it is also possible to work at temperatures up to .100 C.

' In accordance with one embodiment of the process \of the invention, however, it is also possible for the carbon monoxide to .be reacted at elevated pressure. By raising the carbon monoxide pressure within a pressure range between 100 and .600 atm., preferably between Y100. and 300 .atm., certain olefinic rearrangements are suppressed and advantageously normal carboxylic acids, 'i. e. those formed without re-arrangement, are produced in a simple manner. By raising the pressure of carbon monoxide, a reaction which is especially suppressed is the dimerisation of the olefines by .means of which otherwise car'boxylic acids of relatively high molecular weight are formed. Moreover, the migration of the methyl group is prevented, which migration would lead to the formation .of mainly tertiary carboxylic acids instead of normal secondary carboxylic acids. The migration of .the methyl groups, however, takes place mainly with unbranched olefines which do not carry any branching'at the double bond. With this class of olefines, di'mefisition does not play any part, while on the contrary the olefines branched at the double bond show a strong tendency to dimerisation and no migration of methyl groups takes places with these latter olefines.

The course of the reaction becomes particularlyapparent by taking examples of the reaction of two isomeric pentenes: (a) the unbranched pentene-Z, and (b) the Z-methyl butene-2 branched at the double bond.

7 (a) The normal reaction product of pentene-Z would be the two secondary C -carboxylic acids, a-methyl valeric acid (methyl-propyl-acetic acid) and methyl butyric acid (diethyl-acetic acid). carom CH-COOH lHrC-CH:-GH=CHCH:+CO-i-HgO-CHs-OH;

CH3CH2-CH2 CH3 Owing to the migration of methyl groups, however, 'there is also formed a tertiary acid which in certain circumstances is even the main acid, namely a,ec-dirnihy] butyric acid (dimethyl ethyl acetic acid).

CH3 CHr-OHz-+-OOOH (b) The reaction product of the pentene isomer 2- methyl butene-2 branched at the double bond contains -only the single tertiary a,a-dimethyl butyric acid as a C -carboxylic acid. With a low carbon monoxide pressure, however dimerisation to form a branched decene, which then reacts with carbon monoxide and produces ,a mixture of C -carboxylic acids, takes place.

It is possible initially to operate completely in the absence of water when using the process of the invention, =although the presence of water is absolutely necessary according to the general reaction equation RCH=CH-R'+CO+H O RCH --CHR'--COOH 'Water can be added only after the reaction with carbon monoxide according to the process of the invention.

It is advantageous for the boron trifluoride-phosphoric acid catalyst to be prepared in known manner at an elevated temperature, for example about 100 C., that is to say, the boron trifluoride is introduced into, for example, 85% phosphoric acid at 100 C. until saturation is reached.

Tertiary olefines, that is to say, those which are branched at the double bond are, for example, capable of being reacted in a particularly smooth manner with boron trifluoride-phosphoric acid as catalyst.

As an example of the reaction of isobutene or Z-methyl pentene-l with the boron trifluoride-phosphoric acid complex as catalyst, the'operation of the process of the invention at low pressures will be described. For example, if 'a catalyst is used which has been obtained from 240 g. of 85% orthophosphoric acid by saturation at 100 C. with 225 g. of boron trifluoride, and is probably a mixture of 1 mol of monohydroxy fluoroboric acid H(BF OH) and 2 mols of orthophosphoric acid, bound in a complex manner to BF 6 mols of Z-methyl pentene-l are :in this case reacted in an autoclave at a temperature of approximately 4 to C. and a carbon monoxide pressure of 75 to 100 atm. It is advantageous to force in about 1.5 mols of water after each 2 mols of olefine. The reaction proceeds at exceptionally high speed and the carbon monoxide pressure therefore does not fall j any lower as the olefine is sprayed in. After the product has been removed from the autoclave, the residual amount oi-water which is theoretically necessary is then added that altogether 6 mols of water have been added. A clear separation into a lower catalyst layer and an upper mixture of sulphuric acid and boron fluoride.

in which the cost of catalyst is particularly advantageous 4 carboxylic acid layer is then immediately obtained, that is to say, without the addition of more water. The catalyst can be used again for further reactions. In contrast to the process in which concentrated sulphuric acid is used, no regeneration or re-concentration is necessary in this case. However, some boron fluoride always passes into the organic layer, but can easily be washed out with a small amount of water, this water used for washing purposes being sprayed into the autoclave with the next batch. The yields of carboxylic acid produced by the process of the invention are extremely good. It is readily possible to obtain 85 of total acid, of which again consist of the C -carboxylic acid theoretically to be expected.

It is also possible to select other proportions of the constituents for the complex catalyst, for example by starting with 50% phosphoric acid which also is saturated with boron fluoride at 100 C. In such a case, about 4 mols of monohydroxy fiuoboric acid H(BF OH) are used to 1 mol of H PO BF Even with this mixture, the reaction of, for example, 2-methyl pentene-l with carbon monoxide proceeds quite smoothly. The working up is carried out as previously described.

Satisfactory results were also produced when using a catalyst consisting of monohydroxy fluoboric acid prepared by the saturation of water with boron fluoride while cooling with ice. On the other hand, concentrated phosphoric acid when used by itself proves to be completely inactive.

The combination of phosphoric acid and monohydroxy fiuoboric acid is to be considered as equivalent to the' -When reacting 2-methyl pentene-l with a catalystwhich has been prepared from sulphuric acid'by saturation at 100 C. with boron trifluoride, good yield. of carboxylic acids were likewise obtained in a rapic' reaction. The method of operation in such a case war that always the catalyst recovered from the preceding batch or mixture was activated by adding a small amount of fresh catalyst. In this manner, in altogether 9 batches or mixtures, not less than 45 mols of Z-methyl pentene-l (=3800 g.) could be reacted with 7.4 mols of H 80 (=737 g.) and 3.5 mols of BF (=241 g.) with an aver-,, age yield of of carboxylic acids. After these batches, the series of tests was broken off without thereg being any indication of abatement of the catalyst activity. 7

A method of carrying out the process of the invention consists in using a catalyst which does not consist solely of monohydroxy fluoboric acid (owing to the high cost of boron trifluoride) but contains, in addition to boron trifluoride, a less expensive material as the second compent of the complex compound, for example orthophos phoric acid or sulphuric acid. In this connection, it is advantageous for the catalyst to contain only as much boron trifluoride as is necessary for producing an active H PO -BF or H SO --BF complex.

The following examples further illustrate the invention.

Example 1 1 litre of a complex mixture of phosphoric acid and monohydroxy fluoboric acid was introduced as catalyst into an autoclave with a magnetic stirrer mechanism and made of V4A-extra steel and a capacity of 5 litres. This catalyst was obtained by introducing gaseous boron fluoride at C. into 85 phosphoric acid until the saturation point was reached, and had substantially the composition of 2(H PO .BF )+H(BF OH). After introducing carbon monoxide to give a pressure of 100 atm., 480 g. of isobutene (corresponding approximately to 8.5 mols) were injected by means of a pressure pump in the -course of 5 hours, a reaction temperature of 5 to 10' C.

was also injected. when the absorption of carbon nion oxide had ceased, the reaction product was removed and mixed with the residual amount of water (about 4 mols) which was still theoretically necessary; A separation into two layers then took place, and the lower catalyst layer formed was returned to the autoclave again, while the upper carboxylic acid layer was worked up together with the reaction products obtained in following batches.

6.8 kg. of a reaction product were obtained. inthe manner described in ten batches, from altogether 4.8 kg. of isobutene, which product yielded 6.2 kgfof'carboxylic acids and also 600 g. of neutral oil after separation by way of the alkali metal salts. The carboxylic acids were subjected to fractional distillation in vacuo, and the main constituent was found to be 72.5% of trimethyl acetic acidv (B. P. 76.5 C., M. P. 35.5 C.);'13'% of C -acid and 14.5% of acids of higher molecular weight were also found. i

Example 2 465 g. of the complex phosphoric acid-monohydroxy fluoboric acid catalyst described in Example 1 were placed in a V4A-extra autoclave equipped with magnetic stirring and having a capacity of 2 litres, and acarbon into av lower catalyst layer and an upper carboxylic acid layer by adding'the residual amount of water which was still theoretically necessary. The separated catalyst was used again for another 4 batches, so that altogether 30 r'nols of 2-methyl pentene-l were reacted. These 2.5 kg. of olefine yielded 3.9 kg. of a crude product from. which the carboxylic acids were extracted with caustic. potash solution and thereafter liberated again by hydrochloric acid. The yield of carboxylic. acids amounted to 3.4 kg. and there was also 0.5 kg. of neutral oil. Fractional distillation in vacuo in a. packed tower showed that ,0:- dimethyl valeric acid (B. P. ,=ll'l C., n =l.42l0) in an amount of 75% formed the main constituent in the composition of the carboxylic acids, and that there were also 5% of fatty acids of lower. molecular weightand 20%- of fatty acids of higher molecular weight.

Example 3 With a carbon monoxide pressure of 80 atrn..and a reaction temperature of 5 to C., 500 g. (6 mols) of 2-methyl pentene-l were injected by means of a pressure pump in the course of 3 hours, 1.5 mols of water being introduced after each addition of 2 mols of olefine. When the absorption of carbon monoxide had ended, the reaction product was emptied out and worked up in the manner described in Examples 1 and 2. The catalyst recovered was used in three additional batches without it being possible to detect any diminution of the activity.

Altogether 2 kg. (24 mols) of 2-methyl pentene-l were used and there were obtained therefrom 2.4 kg. of fatty acids. They consisted of 75 of a,a-dimethyl valeric acid (B. P. =11l C., n =l.4210), 5% of fatty acids of lower molecular weight and 20% of fatty acids of higher molecular weight. 0.2 kg. of a neutral oil which was not further investigated was also obtained.

this catalyst was apwere placed in a 2 litre -V4A-extra"autoclave and 4 mols Example 4' A catalyst consisting of 430 g, of monohydroxy fluoboric acid prepared by saturating 90, g. of water- ('5 mols) witlr340 g, of boron fluoride (5 mols) at 0 C. was used. 500 g. (6 mols) of Z-methyl pentene-l were sprayed into a 2-.-litre .V4A-extra autoclave with magnetic stirring means at a. carbon monoxide pressure of 90 atm. and a reaction temperature. of 0 to 5 C. over a period of 3 hours,.,'1 mol of water being introduced after each addition of 2 mols of olefine. When the absorption of carbon monoxide was complete, the reaction product was worked up in the manner already described in the earlier examples and the catalyst separated out was used for two further batches.

During the total conversion of 1.5 kg. (18 mols) of 2-methyl pentene-l, 128 kg; of fatty acids and 0.2 kg. of neutral oil were obtained. The carboxylic acids consisted of of a,a-dimethyl valeric acid (B. P. =l.1l C., n ?"=l.42lO) 8%- of fatty acids of lower molecular weight and 22% of fatty acids of higher molecular weight.

Example 5 A complex mixture of sulphuric acid and monohydroxy fluoboric acid was prepared by introducing boron trifluoride into 340 g. of sulphuric acid'at C. to the netic stirring means, the said autoclave being filled with 435 g. of the above-described catalyst and having a car bon monoxide pressure of 80 atrn. maintained therein. 1 mol of water was injected after each additionof'Z mols of olefine. As soon as the absorption of carbou'morroxide was complete, "the reaction product was emptied out and worked up as described inthe earlier examples. The catalyst recovered was used for another 8' batches, and in order to maintain a constant activity an amount of 90g. of fresh catalyst was added before each fresh batch and a corresponding amount of the used catalyst was withdrawn. 7

From altogether 45 mols (3.8 kg.) of 2-methy1 pentene-l, 4.8 kg. of carboxylic acids were obtained, and-the Qcomposition of these acids was, determined by fractional was g.

Example 6 460g. of a catalyst having the. composition -2(H3 BF3)+H BF30H) (450 g.) of 2-ethyl hexene-l were forced in over a period of 4 hours at a temperature of 5 to 10 C. and at a carbon monoxide pressure of 50 atm.

1 mol of water was injected after each 2 mols of olefine. When the product was worked up in the usual manner, 532 g. of carboxylic acids and 55 g. of neutral oil were obtained. Fractional distillation in vacuo showed that the carboxylic acids consisted of 62% of C -acids (B. P. =l25.5 C., n =l.4334), and there were also 8% of fatty acids of lower molecular weight and 30% of I fatty acids of higher molecular weight.

Example 7 isododecene was a mixture of substantially 3 isomeric trimethyl nonenes.

The olefine was reacted with carbon monoxide in a '2 litre V4A-extra autoclave which was charged with 460 g. of the complex phos'phoric-acid-monohydroxy fluoboric acid catalyst, prepared by saturating 85% phosphoric acid with boron fluoride at 100 C. During the introduction of the dodecene, the carbon monoxide pressure was 80 atm. and the temperature 5 to C. Altogether 4 mols (i. e. 672 g.) of olefine were introduced in each batch and 1 mol of water was sprayed in after each 2 Example 8 The olcfine used as starting material consisted of 2- methyl pentene-l, which was reacted at different carbon monoxide pressures. The catalyst consisted of complex mixtures of boron fluoride with sulphuric acid or phosphoric acid which had been obtained by saturating 85% acidsat 100 C. with boron fluoride. The following table shows the resultszwhich were obtained with these catalysts, in one case with a carbon monoxide pressure of 100 atm. and in the other of 300 atm. The raising of the pressure resulted in a pronounced reduction of the dimerisation and thus in the formation of C -carboxlic acids.

Carbon Yield ot-carmon- Total boxyllc acids Car- Catalyst oxide yield, (Percentage of boxylic pressure, percent total yield), acid atm. valeric acid l k- 1504 $8,, 33 3% BFa-Hr-P O4 $88 g; 3

What we claim is:

1. In the process for the production of carboxylic acids by reaction of an olefin with carbon monoxide in the presence of a catalyst, the improvement, facilitating catalyst recovery for reuse, which comprises effecting said reaction by contacting an olefin, having a branched chain at a double bond carbonatom, in the liquid phase with carbon monoxide at a temperature between about 10 and 100 C. under substantially anhydrous condition in ,the presence of a substantially anhydrous catalyst selected from the group consisting of monohydroxyfluoboric. acid, monohydroxyfiuoboric acid mixed with phosphoricacid and. monohydroxyfiuoboric acid mixed with sulfuric acid, and thereafter adding water to the reaction mixture forming a layer containing the formed carboxylic acid, and a separate layer containing separated catalyst suitable for direct reuse.

2. Improvement according to claim 1 in which stoichiometric quantity of water is added.

3. Improvement according to claim 1 in which .said contacting is effected by maintaining said catalyst in a reaction zone, intermittently adding said olefin to said reaction zone in batches for contact with said carbon monoxide, adding a quantity of water in a molar ratio to said olefin of 11.5:2 after the addition of each ,batch of olefin,- and after the total quantity of olefin has been added, adding an amount of water to make up approximately the stoichiometric quantity.

4. Improvement according to claim 1 in which said contacting is effected at a temperature between about 0 and 10 C. I

5. Improvement according to claim 1 in which'said contacting is effected at an elevated pressure below about atmospheres.

6. Improvement according to claim 1 in which'said contacting is effected at a pressure between about 100 and 600 atmospheres.

7. Improvement according to claim 1 in which said catalyst is a catalyst formed by saturating phosphoric acid with boron trifluoride.

8. Improvement according to claim 1 in which said catalyst is a catalyst formed by saturating sulfuric acid with, boron trifluoride.

9. Improvement according to claim 1 in which said catalyst is a catalyst formed by saturating phosphoric acid having a 50-85% concentration with boron trifluoride.

10. Improvement according to claim 1 in which said catalyst is a catalyst formed by saturating sulfuric acid having a 50-85% concentration with boron trifluoride.

11. Improvement according to claim 1 in which .said catalyst is a catalyst formed by saturating phosphoric acid .with boron trifluoride at a temperature of about 100 C.

12. Improvement according to claim 1 in which said catalyst is a catalyst formed by saturating sulfuric acid with boron trifluoride at a temperature of about 100 'C.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,459. Loder Nov. 1,1938

2,593,440 Hagemeyer Apr. 22, 1952 FOREIGN PATENTS 518,682 Belgium n Apr. 15, 1953 

1. IN THE PROCESS FOR THE PRODUCTION OF CARBOXYLIC ACIDS BY REACTION OF AN OLEFIN WITH CARBON MONOXIDE IN THE PRESENCE OF A CATALYST, THE IMPROVEMENT, FACILITATING CATALYST RECOVERY FOR REUSE, WHICH COMPRISES EFFECTING SAID REACTION BY CONTACTING AN OLEFIN, HAVING A BRANCHED CHAIN AT A DOUBLE BOND CARBON ATOM, IN THE LIQUID PHASE WITH CARBON MONOXIDE AT A TEMPERATURE BETWEEN ABOUT -10* AND 100*C. UNDER SUBSTANTIALLY ANHYDROUS CONDITION IN THE PRESENCE OF A SUBSTANTIALLY ANHYDROUS CATALYST SELECTED FROM THE GROUP CONSISTING OF MONOHYDROXYFLUOBORIX ACID, MONOHYDROXYFLUOBORIC ACID MIXED WITH PHOSPHORIC ACID AND MONOHYDROXYFLUOBORIC ACID MIXED WITH SULFURIC ACID AND THEREAFTER ADDING WATER TO THE REACTION MIXTURE FORMING A LAYER CONTAINING THE FORMED CARBOXYLIC ACID, AND A SEPARATE LAYER CONTAINING SEPARATED CATALYST SUITABLE FOR DIRECT REUSE. 